1. Field of the Invention
This invention relates generally to bits for drilling and dressing holes and, more particularly, to a diamond grit coated drill and reamer.
2. Related Art
In recent years, the use of fiber reinforced composite materials has been steadily increasing in many industries due to its lightweight and strength. As the use of such materials expands, there will be an increased need for a cost effective method of producing high quality holes in such materials with dimensions which are within narrow tolerances.
A number of problems arise in using known drilling and grinding techniques to produce holes in fiber reinforced composite materials. These problems include delamination and splintering of the material and fiber breakout. Such phenomena are unacceptable in many applications for a number of reasons, including weakening of the structure through which the hole extends. Another reason is that in some applications the rear of the composite material cannot be easily accessed to prevent delamination and splintering or to remove the splintered material. For example, in long length fiber reinforced composite tubes, the inner surface of the tubes cannot be efficiently accessed to prevent fiber breakout or to remove the splintered material.
One conventional solution is to use special drill bits in combination with some kind of backing support. This approach is typically used with drill bits that rely on a sharp cutting edge. This is because these types of drill bits generally delaminate or fray the back side of the composite material as the drill bit is breaking through unless there is some support that keeps the backside surface in compression. Many cutting edge designs have emerged to eliminate the need for this backing support, but none have succeeded. For some structures, such as small diameter tubes, backing supports are not cost effective or easily used.
Another conventional solution is to implement a Computerized Numerical Controlled (CNC) mill in a two step operation. First, an undersized hole is drilled with a drill that does not cause excessive delamination. Second, the CNC mill enlarges the hole using a small diamond coated router. The desired size is achieved using a circle interpolation method. To be cost effective for the production machining of composite tubes, this method would require a large CNC mill to cover the full length of the tube. Even with a large mill, multiple set-ups and a trained machinist are required. Thus, the CNC mill approach is not cost effective for applications such as making repeatable, accurate, and clean holes in fiber reinforced composite tubes.
What is needed is a drill bit that does not require backing support or a CNC mill. The drill bit cannot cause fraying, splintering, fiber breakout, or delamination.